1. Field of the Invention
The present invention relates to exposure apparatuses, exposure methods and device manufacturing methods, and more particularly to an exposure apparatus and an exposure method to expose an object with an energy beam via an optical system, and a device manufacturing method that uses the exposure apparatus or the exposure method.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as semiconductor devices (integrated circuits or the like) or liquid crystal display elements, an exposure apparatus such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper), or a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner)) is mainly used. This type of the projection exposure apparatus has a stage device that holds a substrate such as a wafer or a glass plate (hereinafter, generically referred to as a wafer) and drives the wafer along a predetermined two-dimensional plane.
In order to perform high-precision exposure, the high-precision positional controllability of a stage is required for the stage device, and in order to improve throughput of the exposure operation, higher speed and higher acceleration of the stage are also required. To cope with these requirements, in recent years, a stage device that controls the position of a wafer within a two-dimensional plane using a planar motor by an electromagnetic force drive method has been developed (e.g. refer to U.S. Pat. No. 6,437,463).
The integration degree of the semiconductor devices is gradually increased, and high-precision position controllability of a wafer that is subject to exposure used in a projection exposure apparatus is required, and as the premise, it is required to measure the position of a wafer stage on which the wafer is mounted, with high precision.
Further, for example, in the fifth embodiment of U.S. Patent Application Publication No. 2008/0094594, the exposure apparatus is disclosed in which encoder heads are placed inside a recessed section formed on the upper surface of surface plate. In the exposure apparatus of U.S. Patent Application Publication No. 2008/0094594, positional information of a wafer stage is measured with high precision by making measurement beams be incident on a two-dimensional grating placed on the wafer stage from directly below.
However, if the planar motor in which the wafer stage has a mover and the surface plate has a stator as disclosed in U.S. Pat. No. 6,437,463 is applied to the exposure apparatus in which the encoder heads are placed inside the surface plate as disclosed in the fifth embodiment of U.S. Patent Application Publication No. 2008/0094594, there is a possibility that the measurement accuracy of the encoder system is degraded owing to a reaction force that acts on the surface plate when the wafer stage is driven.
Meanwhile, the wafer increases in size every ten years and a 300 mm-wafer with a diameter of 300 mm is currently mainstream, and now the coming of age of the 450 mm-wafer with a diameter of 450 mm looms near. Consequently, it is certain that a wafer stage on which a wafer is mounted and a surface plate that forms a guide surface used on movement of the wafer stage increase in size, and therefore there is a concern that the maintenance becomes difficult.